The invention relates to a clutch transmission, in particular a dual-clutch transmission, with a hydraulic circuit for controlling and cooling the clutch transmission, in particular the dual-clutch transmission, in particular of a motor vehicle, with two clutch cylinders and a plurality of switching cylinders which can preferably be actuated from both sides.
Dual clutch transmissions are preferably used in passenger cars. A dual clutch transmission generally includes two coaxially disposed transmission input shafts, which are each associated with a sub-transmission. A clutch is associated with each of the transmission input shafts, via which the transmission input shaft of the respective sub-transmission can be frictionally coupled to the output of an engine, preferably an internal combustion engine of a motor vehicle. A first of the two sub-transmissions typically includes the odd gears, whereas a second of the two sub-transmissions includes the even gears and the reverse gear.
Typically, one of the sub-transmissions is active while driving, which means that the transmission input shaft associated with this sub-transmission is coupled to the engine via its associated clutch. A gear providing a current gear ratio is engaged in the active sub-transmission. A controller determines whether the next higher or next lower gear is to be engaged depending on the driving situation. This gear which is probably used next is selected in the second, inactive sub-transmission. When changing gears, the clutch of the inactive sub-transmission is engaged, while the clutch of the active portion is disengaged. Preferably, opening the clutch of the active sub-transmission and closing the clutch of the inactive sub-transmission overlap so that the flow of force from the engine to the drive shaft of the motor vehicle is interrupted not at all or only briefly. As a result of the gear change, the previously active sub-transmission becomes inactive, while the previously inactive sub-transmission becomes the active sub-transmission. Thereafter, the gear expected to be used next can be engaged in the now inactive sub-transmission.
The gears are engaged and disengaged via elements, preferably via the shift rails that are actuated by hydraulic cylinders, also known as switching cylinders, which have already been mentioned above. The hydraulic cylinders are preferably formed as double-acting hydraulic cylinders, in particular synchronous cylinders or differential cylinders, so that preferably two gears may be associated with each switching cylinder. Alternatively, single-acting hydraulic cylinders may also be provided. The hydraulic cylinders operating the elements, in particular the shift rails, are also referred to as gear selector cylinders. A gear selector cylinder designed as a synchronous cylinder to which in particular two gears are assigned, has preferably three switching positions, wherein in a first switching position a first defined gear is engaged, in a second switching position another defined gear is engaged, and in a third switching position none of the two above-mentioned gears is engaged.
The clutches associated with the two sub-transmissions are also hydraulically actuated, Le. closed or opened. Preferably, the clutches each close when hydraulic pressure is applied, whereas they open when no hydraulic pressure is applied, i.e. when pressure is relieved in a hydraulic cylinder associated with the respective clutch which is also referred to as clutch cylinder, as mentioned above.
In addition, the operation of a dual clutch transmission is known per se and will therefore not be discussed here in detail.
The structure and the operation described in the preceding paragraphs apply preferably also to or are related to the subject matter of the invention.
As already indicated, dual clutch transmissions are controlled or regulated as well as cooled by a hydraulic circuit. This hydraulic circuit, or subassemblies thereof, and methods associated therewith are the object of the invention.
Conventional clutch transmissions as disclosed, for example, in the European patent EP 1 486 693 131, also include a cooler for cooling the hydraulic medium pumped by a pump. Under cold ambient conditions, a thermostatic bypass valve is provided in the cooler for a rapid warm-up of the clutch transmission. In the conventional clutch transmission, the hydraulic medium should therefore not be cooled, but bypass a cooler so as to more quickly reach, for example, an operating temperature.
Providing a bypass with a differential pressure valve is known to protect, for example, a pressure filter against excessively high pressures.